1. Field of the Invention
The present invention relates to a device control apparatus, a device control method and a computer program, and more particularly, to a device control apparatus, a device control method and a computer program that control operations unique to other devices using a digital interface for signal transmission.
2. Description of the Related Art
A high definition multimedia interface (HDMI) has been widely used as a digital interface for transmission of a video signal and an audio signal. The HDMI is a digital visual interface (DVI) standard, which is a connection standard of a personal computer (PC) and a display, with an audio transmission function or a copyright protection function for audio visual (AV) devices. The HDMI standard is described in detail in the High-Definition Multimedia Interface Specification Version 1.3.
An HDMI standard interface is capable of bidirectional transmission of a control signal. Accordingly, for example, a television receiver can transmit a control signal to an output device such as a set top box (STB) or a video disc player connected via the HDMI cable. The transmission of the control signal from the television receiver enables a user to manipulate an overall AV system using a remote controller of the television receiver. While signals transmitted via a transmission cable conforming to the HDMI standard include a control instruction for controlling devices, as well as a response to the instruction, a signal indicating states of the devices, and the like, the signals are collectively referred to as a control signal in this disclosure.
In the HDMI standard, inter-device control using consumer electronics control (CEC) is defined. The CEC is one transmission line prepared in the HDMI standard, and performs bidirectional data transmission. Using this CEC line, various controls become possible based on unique physical and logical addresses assigned to each device present in an HDMI network. For example, when a user is viewing a digital broadcast using a television receiver, if a video disc player connected via the HDMI cable performs reproduction, the television receiver is automatically switched to an input to which the video disc player is connected. Menus displayed in this video disc player, a power on/off, and the like can be manipulated using the remote controller of a television receiver.
The HDMI standard defines that a maximum of ten devices, including a television receiver, are allowed to be connected. Accordingly, a maximum of nine external devices can be connected to one television receiver. If the nine external devices are connected to the television receiver, any of the devices can be manipulated using a remote controller.
In the HDMI standard, <Active Source> is defined as a CEC message for specifying a device that is displaying a video on a television receiver. According to this definition, for example, when a user manipulates a Play button of a video disc player that is compliant with the HDMI standard, the video disc player outputs an AV stream if the player is in a state in which the player can output a stable video signal (i.e., an active state). Further, the video disc player broadcasts an <Active Source> message indicating that the video disc player is an active device.
Here, “broadcast” refers to simultaneous transmission of a signal whose transmission destinations are all devices rather than a specific device. The television receiver and other external devices to which the <Active Source> message is broadcast switch a path to reproduce AV streams output from the video player.
Thus, the HDMI standard defines that a device that initiates a display of a video in a television receiver broadcasts an <Active Source> message to other devices in a network. Further, the <Active Source> message is one CEC message defined in the HDMI standard.
In a related art, as described in, for example, Japanese Patent Laid-open Publication No. 2008-35399, a function of changing a reproduction sound field according to genre information of an electronic program guide (EPG) obtained in a television receiver has been realized as HDMI-CEC control. Using this function, the EPG genre information flows into the HDMI-CEC line upon initiation of reception of a program to be viewed on the television receiver or upon a change of the program. When an audio player device called, for example, an AV amplifier, receives the genre information flowed into the CEC line, the reproduction sound field is set according to the genre information.
Adjustments such as, when a sports program is viewed, a play mode in which realistic sensation of the sports program is obtained is set, and when a news program is viewed, a play mode in which voice (speaking voice) is easy to listen to is set becomes possible.